Artificial cardiac pacemakers: Current concepts

Electrocardiographic "pacemaker pseudo-spikes" and radio frequency interference

PURPOSE

To present a case of apparent interference of an ECG monitor by radiofrequency interference (RFI) and to provide a brief review of RFI issues to critical care medicine.

CLINICAL FEATURES

A 74-yr-old woman, with an implanted pacemaker, underwent major spinal surgery. In the post-anaesthesia care unit, the cardiac monitor demonstrated graphic evidence of pacemaker malfunction but there was no apparent effect on the patient. Investigation by the hospital's biomedical personnel led to the conclusion that RFI was being interpreted by the monitor as abnormal pacemaker activity.

CONCLUSION

With the emergence of portable, battery-operated communication devices, there is an increased risk of RFI within hospitals. Antennas and repeaters are required to receive and boost the signal levels of these devices to improve signal quality. They are located throughout hospitals and may be situated near patient care areas. Patient monitors may receive these signals, misinterpret them as being patient-generated and output erroneous information. In the case described, the monitor was presented with RFI signals and interpreted as pacemaker spikes, generating a tracing suggestive of pacemaker malfunction. Troubleshooting strategies and minimizing the potential impacts of RFI on patient monitors are discussed.

Effect of myocardial revascularization and vein graft blood flow on pacing function

The effect of myocardial revascularization and vein graft blood flow on pacing function was determined in nine patients undergoing aortocoronary bypass. Pacing variables including threshold, current, and resistance were measured with a pacing system analyzer during intermittent pacing with a transluminal bipolar ventricular pacing probe. Pacing function was analyzed immediately before cardiopulmonary bypass (CPB) and compared with measurements taken eight minutes after full flow through the vein grafts had been established. Comparison of these two times showed a significant decrease in resistance, P < 0.003, and threshold, P < 0.03. After the second measurement, left anterior descending (n = 8), or right coronary (n = 1) vein graft blood flow was interrupted. Pacing variables were analyzed at one minute, two minutes, and four minutes following vein graft clamping; and a final set of measurements was obtained one minute following release of the vein graft clamp. Threshold increased but did not reach statistical significance. Resistance increased significantly: P < 0.03. All values returned to baseline following release of the vein graft clamp and full return of blood flow. The results of this study suggest that pacing function measurements are sensitive to changes in vein graft blood flow and may provide useful information about the condition of the myocardium, especially immediately prior to weaning from CPB.